[html5] validator.nu Web GUI -- How to validate against XHTML5?

[jama]

On 06.11.2012 09:46, Michael[tm] Smith wrote:
> It works for me as expected without reporting that error. Do you have 
> the "Be lax about HTTP Content-Type" option checked when you feed it 
> the .html file?
Ah, I forgot to check this option. The .html file now validates (with 
two warnings, but they're to be expected).

Well then! For now, when validating files against XHTML5, I'll make sure 
to use the file extension .xhtml on my files or use validator.nu with 
"Be lax about HTTP Content-Type" checked.

Btw, and kinda off topic, can I properly validate polyglot XHTML5 files 
as well with validator.nu (or the W3C version of it)?